Abstract
The conversion of methane to ethylene has been investigated in a micro-DBD reactor with electrodes containing charge injector parts and excited with a negatively nano-second pulse voltage superimposed on a positive dc voltage. The effect of changing the characteristics of pulsed voltage such as pulse rise time (5–7 ns), total pulse width (12–14 ns), and pulse fall time (5–7 ns) on generation rate and products selectivity of the methane plasma has been studied. The kinetic model includes twenty species (electron, ions, radicals, and neutrals). The results showed that change in input pulse shape changes the generation rate and selectivity of neutral products. The rate of voltage change during pulse on-time significantly changed the instant C2H4 selectivity. With increasing the pulse rise and fall times the ethylene selectivity decreases, while the hydrogen selectivity increases. Results also showed that the electron reactions are dominant conversion channels during pulse on-time, while they had lower contributions in conversion progress during pulse off-time and the conversion process during this period is mainly governed by the radical reactions.
Highlights
IntroductionIncreasing the energy efficiency and selectivity of product species can be achieved by optimisation of plasma reactors and making synergy between plasma systems and other previously common process approaches
Atmospheric-pressure non-thermal plasmas, providing formation and reaction of radicals in ambient condition, has recently received a growing attention in manufacturing processes and chemistry applications such as surface modification and material synthesis [1–4], conversion of waste and natural gases [5, 6], and N2 fixation into ammonia or NOx [7, 8].SA 5005, Australia 3 Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O.Box 513, 5600 MB Eindhoven, The Netherlands1 3 Vol.:(0123456789)Plasma Chemistry and Plasma Processing (2022) 42:619–640the energy efficiency of these plasma processes remains a key bottleneck against its wider industrial acceptance
This figure implies that any change in voltage profile, which can be established by varying pulse parameters, can directly change rates of electron reactions that have the main roles in the plasma reaction mechanism
Summary
Increasing the energy efficiency and selectivity of product species can be achieved by optimisation of plasma reactors and making synergy between plasma systems and other previously common process approaches. Methane activation in discharge plasma is a rapidly expanding research topic in both science and engineering. This includes life cycle assessment and eco-efficiency analysis at industrial scale in process engineering field [10, 11], and making synergy between plasma and catalysts to control the selectivity of products, product yield and conversion rate in chemistry field [12–15]. The focus is on the design of new plasma reactors and application of different discharge types for the purpose of controlling and tuning the reaction mechanism, heat transfer rate, and, more important, increasing energy efficiency [16–21]. The methane conversion processes are classified in two main areas: (i) oxidative conversion to syngas or C1-oxygenates and (ii) non-oxidative conversion to C 2H4 and C3H6 as the desired products
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